1. Field of the Invention
The present invention relates to a device and a method for use on a seabed to collect and record signals during the execution of marine seismic off-shore explorations. Basically, the invention concerns seismic exploration of the substratum offshore, where pressure and shear waves from the substratum are measured in response to the releasing of pressure and/or shear wave energy.
2. Description of the Related Art
Marine seismic exploration is usually carried out by a seismic cable provided with several hydrophones being towed at a certain depth. Pressure waves are released in the vicinity of the cable in several ways. This usually takes place by means of air guns. The pressure wave energy travels downwards through the substratum, but parts of the pressure waves are reflected from areas where there are acoustic impedance features in the substratum. The hydrophones record the reflected pressure waves in the water and transform this information into electric signals which are received and processed on the seismic ship which tows the cable. Using this method, only reflected and/or converted shear to pressure wave energy is recorded. However, it is known that down in the formation both pressure waves and shear waves will be reflected. The shear waves do not travel in water and cannot therefore be detected by a hydrophone cable. Moreover, with today's conventional hydrophone technology, it is not possible to detect the directions of the measured signals, and this severely complicates the possibilities of three-dimensional data collection.